PA — Preamble: 4 or more symbols of Idle.
SD — Starting Delimiter: The symbols 'J' and 'K'.
FC — Frame Control: 2 symbols describing what type the token is.
ED — Ending Delimiter: two 'T' symbols.

A station gains the right to transmit its information onto the medium when it detects a token passing on the medium. The token is a control signal comprised of a unique symbol sequence that circulates on the medium following each information transmission. Any station, upon detection of a token, may capture the token by removing it from the ring. The station may then transmit one or more frames of information. At the completion of its information transmission, the station issues a new Token, which provides other stations the opportunity to gain access to the ring.